The double-edged oxygen: Harnessing anionic redox in lithium-rich manganese-based cathode materials

Lithium-rich manganese-based layered oxides (LRMOs) have emerged as promising high-capacity cathode materials for next-generation lithium-ion batteries due to their ability to leverage both transition-metal cationic and lattice oxygen anionic redox reactions. This dual redox mechanism, facilitated by Li-excess-induced local coordination environments such as Li–O–Li and Li–O–Mn motifs, enables enhanced reversible specific capacity beyond conventional cathode materials. Despite their high energy density and resource advantages, LRMOs face significant challenges including initial-cycle irreversible capacity loss, voltage decay, structural degradation, gas evolution, and interfacial instability during cycling. In this review, we systematically examine the mechanistic origins of oxygen redox activity, the multiscale structural degradation processes, and the coupled cationic–anionic charge compensation. We further discuss defect engineering strategies for stabilizing lattice oxygen, optimizing Li diffusion pathways, and improving electronic/ionic kinetics, alongside surface/interface engineering approaches including inorganic coatings, ion-conductive layers, and electrolyte modifications to mitigate interfacial side reactions. By integrating insights from electronic structure, crystallography, and electrochemical characterization, this review highlights rational design principles to enhance the reversibility, cycling stability, and rate capability of LRMOs, providing guidance for the development of high-energy, sustainable, and long-lasting lithium-ion battery cathodes.